VA's Office of Public Health has investigated the potential exposure to Agent Orange among crew members of C-123 aircraft used previously in spraying missions during the Vietnam War.
Although residual TCDD – the toxic substance in Agent Orange – may be detected in C-123 aircraft by sophisticated laboratory techniques many years after its use, the Office of Public Health concluded that the existing scientific studies and reports support a low probability that TCDD was biologically available in these aircraft. Therefore, the potential for exposure to TCDD from flying or working in contaminated C-123 aircraft years after the Vietnam War is unlikely to have occurred at levels that could affect health.
To address the concerns expressed by crew members, the Office of Public Health reviewed available scientific reports and peer-reviewed literature related to potential adverse health effects, such as:
- Physical properties of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)
- Routes of exposure (inhalation, ingestion, dermal) and bioavailability (ability to enter the body) of TCDD over extended periods
- Known levels of safe exposure and threshold levels of TCDD toxicity
Properties of TCDD
TCDD may be inhaled as an aerosol. The reports and literature demonstrated that in the vapor stage, TCDD has an atmospheric lifetime of only about three days. Dried TCDD on interior aircraft surfaces does not aerosolize when exposed to temperatures found inside aircraft during any conceivable use. There is a low probability that dried TCDD would aerosolize during routine crew use and present a risk to health by inhalation. Also, there are no data from the U.S. Air Force or other sources confirming dioxins in air samples taken from post-Vietnam C-123 aircraft.
Routes of exposure
Ingestion as a route of exposure on these aircraft would require that TCDD would need to have entered the mouth through contaminated food or water or by hands contaminated with TCDD. There is a low probability that transfer of TCDD in food or water or from hand-to-mouth could occur among these crew members, especially given that the sampling for TCDD on the aircraft surfaces required use of a solvent (hexane) to displace and dissolve any residue.
Solid TCDD can be extremely stable in the absence of direct sunlight. Once TCDD dries on hard surfaces, such as on an aircraft, it does not readily cross through human skin. Even if the dried material were to come into contact with perspiration or oils on skin, the skin would act as a barrier prohibiting further penetration of TCDD. There is a low probability that TCDD penetrated through the skin of these aircrews.
Scientific review and analysis
The Office of Public Health reviewed the following studies and reports, and will continue to review new findings relevant to this issue as they become available.
Air Force sampling reports
- "Aircraft Sampling: Westover AFB, MA." Prepared by W.W. Conway, USAF Occupational and Environmental Health Laboratory, Brooks AFB, TX; 1979.
- "Memorandum for 645 MedGrp/SGB: Consultative Letter AL/OE-CL-1994-0203, review of Dioxin Sampling results from C-123 Aircraft, Wright-Patterson AFB, OH and Recommendations for Protection of Aircraft restoration Personnel." (444 KB, PDF) Prepared by WH Weisman and RC Porter, Armstrong Laboratory, Brooks AFB, TX; 1994.
- "Memorandum for HQ AFMC/SGC: Consultative Letter, AL/OE-CL-1997-0053, Cleanup of Contaminated Aircraft, Aerospace Maintenance and Regeneration Center." (140 KB, PDF) Prepared by RC Porter, Armstrong Laboratory, Brooks AFB, TX; 1997.
- "Dioxin and Herbicide Characterization of UC-123K Aircraft – Phase I." Prepared for Director of Operations, 505 Aircraft Sustainment Squadron and Hazardous Waste Program Manager, 75CEG/CEVC, Hill AFB, UT (prepared by Select Engineering Services, Layton, UT); 2009.
- Buffler PA, Ginevan ME, Mandel JS, Watkins DK. The Air Force health study: an epidemiologic retrospective. Ann Epidemiol 2011; 21:673-87.
- Diliberto JJ, Jackson JA, Birnbaum LS. Comparison of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) disposition following pulmonary, oral, dermal, and parenteral exposures to rats. Toxicol Appl Pharmacol 1996; 138:158-68.
- Karch NJ, Watkins DK, Young AL, Ginevan ME. Environmental fate of TCDD and Agent Orange and bioavailability to troops in Vietnam. Organohalogen Compounds 2004; 66:3689-94.
- Keenan RE, Paustenbach DJ, Wenning RJ, Parsons AH. Pathology reevaluation of the Kociba et al. (1978) bioassay of 2,3,7,8-TCDD: implications for risk assessment. J Toxicol Environ Health 1991; 34:279-96.
- Michaud JM, Huntley SL, Sherer RA, Gray MN, Paustenbach DJ. PCB and dioxin re-entry criteria for building surfaces and air. J Expo Anal Environ Epidemiol 1994; 4:197-227.
- Newton M, Norris LA. Potential exposure of humans to 2,4,5-T and TCDD in the Oregon coast ranges. Fundam Appl Toxicol 1981; 1:339-46.
- Weber LW, Zesch A, Rozman K. Penetration, distribution and kinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin in human skin in vitro. Arch Toxicol 1991; 65:421-8.
- Young AL, Giesy JP, Jones PD, Newton M. Environmental fate and bioavailability of Agent Orange and its associated dioxin during the Vietnam War. Environ Sci Pollut Res Int 2004;11:359-70.
Risk assessment reports
- Doull J. Acceptable levels of dioxin contamination in an office building following transformer fire. Washington, DC: National Academy Press, 1988.
- Kim NK, Hawley J. Risk assessment: Binghamton State Office Building. (285 KB, PDF) Albany, NY: New York State Department of Health, 1982.
- University of California [Davis]. Department of Environmental Toxicology. Risk Science Program (RSP). Intermedia transfer factors for contaminants found at hazardous waste sites: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD). (118 KB, PDF) Sacramento, CA: Department of Toxic Substances Control, 1994.
- United States Air Force (USAF) School of Aerospace Medicine. Consultative Letter, AFRL-SA-WP-CL-2012-0052, UC-123 Agent Orange Exposure Assessment, Post-Vietnam (1972-1982). (2.3 MB, PDF) Wright-Patterson Air Force Base, Ohio: Air Force Research Laboratory, Department of the Air Force, April 27, 2012.
Summaries of TCDD
- 2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) - US Environmental Protection Agency, Air Toxics Website
- Chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans chronic toxicity summary (46 KB, PDF) - California Environmental Protection Agency, Office of Environmental Health Hazard Assessment
- Intermedia transfer factors for contaminants found at hazardous waste sites: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) (118 KB, PDF) - California Department of Toxic Substances Control; Risk Science Program, University of California, Davis
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